Force balance lever mechanism

ABSTRACT

A force balance lever system for controlling a positionable output member as a square or square root function of a variable input force.

United States'Patent 1191 DRAIN sou/ms AT gems REGULATED co/vs TANT 1PRESS P 'FL u/o SUPPL Y McCombs, Jr. 14 1 Jan. 30, 1973 1541 FORCEBALANCE LEVER 2980,06 1 4/1961 1111111101111 ..91/382 MECHANISM3.045.983 7/1962 1 75 inventor: Howard Lewis McLombs Jr. South I lBendlnd. 3393,1506 7/1968 Magnum ..91 47 [73] Assignee: The BendixCorporation Primary Examiner paul Maslousky [22] Filed: March 24,1971Attorney-Gordon H. Chenez and Flame, Hartz," pp No: 127,700 Sm1th andThompson v [57] ABSTRACT [52] [1.8. CI. ..91/47, 91/382, 74/522 I 5 m, 51 A force balance lever system for controlhng a pos1- [58] Field ofSearch ..91/47, 382; 74/522 tionable output member as a square or squareroot I 1 function of a variable input force. 56 R fer n es C'ted 1 e e cl '16 Claims, 5 Drawing Figures UNITED STATES PATENTS 2,764,868 10/1956Watson/ct a1 ..91/47 FORCE BALANCE LEVER MECHANISM BACKGROUND OF THEINVENTION Numerous prior art control devices require reliable andaccurate control over an output control signal as a predeterminedfunction of a variable control input signal as, for example, incombustion engine governor devices wherein it may be desired toestablish the position of a fuel control member as a predeterminedfunction of engine speed. In such a case, engine driven centrifugalweights normally generate a control input force which varies as afunction of engine speed squared as will be recognized by those personsskilled in the art. As a result of the squared function of input forcerelative to engine speed, an attempt to control the position of anoutput member as a linear function of engine speed necessitates theuse'of cams, multiple lever networks, or the like, to compensate for thesquared relationship of input force to engine speed which, in turn,causes a corresponding increase in control complexity and associatedproblems in control reliability, size,

weight, accuracy as well as manufacturing cost.

In other control applications, it may be desirable to position thecontrol output member as a non-linear function as, for example, thesquare, of a control input signal representing a condition of operationother than engine speed in which case the control network complexitysuffers accordingly.

SUMMARY OF TIIE INVENTION The present invention has for an object toprovide a simple and reliable force balance system wherein the outputposition of a movable control member is reliably and accuratelycontrolled as a predetermined function of the square or square root of acontrol input signal.

It is an object of the present invention to provide a force balancesystem for an engine governor and particularly adapted for use incontrolling a positionable member as a predetermined function of thesquare root of a control input force derived from engine rotationalspeed.

Other objects and advantages of the present invention will be apparentto those skilled in the art from the following description taken withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 represents a schematic drawingof an engine speed sensing device embodying the force balance system ofthe present invention;

FIG. 2 represents a schematic drawing of a portion of FIG. 1 showing amodified form of the force balance system;

FIG. 3 represents a cross sectional view taken on line 3-3 of FIG. 2;

FIG. 4 represents a series of curves having an input force F, vs. outputposition y relationship.

FIG. 5 represents a modified form of FIG. I wherein an output positionsignal varies as the square of an input position signal.

I DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings andFIG. 1 in particular, numeral designates a casing or housing defining aspur gear 32 suitably mounted on a rotatable support chamber 22 and acylinder 24. A differential area piston 26 slidably carried in cylinder24 is provided with a shaft 28 extending axially therefrom into chamber22 and slidably carried by housing 20. A rack portion 30 formed in shaft28 is adapted to mesh with a shaft 34 the rotational position of shaft34 providing an output control signal for use in actuating a fuelcontrol member or the like, not shown.

The differential area piston 26 has a smaller effective area exposed tofluid at a substantially constant pressure P vented thereto via apassage 36 leading from a pressurized fluid supply source 38. Aconventional fluid pressure regulator 40 suitably connected to passage36 downstream from source 38 operates in a well known .manner toregulate pressure P The opposite larger effective area of piston 26 isvented to passage 36 via a passage 42 containing a restriction 44. Adischarge passage 46 communicates passage 42 downstream from restriction44 to chamber 22 which chamber is vented via a passage 48 to a fluiddrain source 50 at relatively low drain fluid pressure P,,. A flappervalve 52 connected to and actuated by a lever 54 is adapted to coactwith the discharge end of passage 46 to vary the effective flow areathereof and thus the fluid pressure P imposed on the piston 26 which, inturn, determines movement of the same.

The lever 54 is provided with a yoke portion having arms 56 and 58 eachof which arms are suitably pinned for pivotal movement on a fixedsupport 60. A variable input force F imposed on lever 54 by a stem 62loads lever 54 in a clockwise direction as viewed in FIG. 1. The stem 62is slidably carried for axial movement on a pin 64 integral with arotatable table 66. A pair of centrifugal weights 68 pivotally mountedon table 66 are rotatable therewith and are provided with arms 70 whichengage a collar 72 integral with stem 62. The rotatable table isprovided with a stub shaft 74 suitably mounted for rotation in housing20 and having a gear 76 fixedly secured thereto. The gear 76 is suitablyconnected to and driven by conventional driving linkage, not shown,attached to and rotated by a combustion engine, not shown, therotational speed of which is to be measured. The centrifugal weights 68generate a force which is a square function of the rotational speed oftable 66 and thus speed of the engine driving the same. The centrifugalweights 68 bear against collar 72 thereby urging stem 62 against lever54 loading the same with force F A force F, is imposed on lever 54 inopposition to force F by a pair of rollers 80, each of which rideagainst associated arms 56 and 58 of lever 54. The rollers 80 aremounted for rotation on a pin or shaft 82 carried by a lever 84. Aroller 86 having a peripheral groove 88 is suitably pinned for rotationon lever 84 in axially spaced apart relationship to rollers 80. Thegroove 88 mates with a fixed track 90 along which roller 86 is guided.The lever 84 is attached to shaft 28 via a link 92 thereby assuming aposition longitudinally in accordance with the position of piston 26.

The force F is derived from a constant reference force F, generated by acompression spring 94 interposed between an adjustable spring retainer96 threadedly secured to housing 20 and a plate 98. The plate 98 issuitably pinned for pivotal movement on a fixed support 100. A pluralityof conventional temperature responsive discs or capsules 102 may beinterposed between spring 94 and retainer 96 to compensate forvariations in the rate of spring 94 caused by changes in temperature ofthe fluid surrounding spring 94 to thereby maintain the output force ofspring 94 at a constant predetermined value regardless of temperaturevariations.

The reference force F is transmitted to lever 84 via a roller 104 whichissuitably mounted for rotation on a pin or shaft 108 which shaft 108 issecured toa yoke member 110. The roller 104 is grooved to mate with atrack 106 integral with plate 98. The yoke member 110 is secured via asuitable ball and socket connection 1 12 to an adjustable stem 114threade'dly secured to housing thereby providing adjustment of roller104 for control calibration purposes.

Referring to FIG. 2, the embodiment disclosed therein includes theaddition of an adjustable roller positioned as a function of a variablecondition of operation such as an engine operating temperature forvarying the effective reference force F imposed on lever 84. To thatend, a pair of rollers 116 and a roller 118 interposed therebetween arerotatably mounted on a pin or shaft 120 in spaced apart relationship.The shaft 120 is secured to a yoke member 122 suitably secured to andactuated by a conventional condition responsive device generallyindicated by 124 adapted to respond to a suitable input signal such as aengine operating temperature and position yoke member 122 as a functionof the input signal. The roller 118 is suitably grooved to mate withtrack 106 on plate 98 and rollers 116 are adapted to ride againstcorresponding arms of a yoke portion 126 of a lever 128 suitably pinnedfor pivotal movement on a fixed support 130. The yoke 110 carryingroller 104 which is adapted to transmit force from yoke portion 126 tolever 84 is modified to accommodate a pair of rollers 132 are identifiedas 1,, l and l the fixed axial spacing of rollers 80 and 86 identifiedas x and the output position or travel of piston 26 identified as y. Fora balanced condition of the force lever network of FIG. 1, the followingrelationships exist.

F,l,= F y therefore F l ly and F (y/l,) F 1 F,l F x therefore F =F,(l,/x) 2 I, I =x+ y therefore l =x+ 6l By substitution F F (x y l,)/xSubstituting (4) into (I) 2 l/MD) 1/ 2) )y Let a l and equation 7becomes 2 r/ 2) Y Let a A and equation 7 becomes F2: r/ 112) y r/ 2) Leta 2 and equation 7 becomes 2=( 1/ 2) y 1/ 2) )y 0) Making F,, x and 1equal to unity and deleting constants, equations 8, 9 and 10 may berespectively reduced to Substituting F K N and F KT= K 0 wherein Nrepresents engine rotational speed, K a constant, T is atmospherictemperature in degrees Fahrenheit and K is K/S l9 to correct to absolutetemperature, equation 14 may be rewritten It will be noted from equation(15) that the output position y of piston 26 represents enginerotational speed corrected for atmospheric temperature as will berecognized by those persons skilled in the art.

Assuming the input force F 2 to increase as a result of an engine speedvariation, the lever 54 is unbalanced causing flapper 52 to move in anopening direction which, in turn, causes a corresponding drop inpressure P, and movement of piston 26 toward the left as viewed inFIG. 1. The lever 84 follows piston 26 thereby causing roller 88 to movealong track 90 and rollers to move along lever 54 which, in turn,increase the effective lever arms I; and y through which the forces Fand F respectively, act.

The lever 84 being loaded by force F tends to pivot about the pointofcontact of roller 86 and track 90 as a result of the increase ineffective lever arm 1 thereby producing a corresponding increase inforce F a which, in combination with the increase in effective lever army, results in a force moment balance on lever 54 which, in turn,stabilizes flapper 52 thereby reestablishing the pressure P required tostabilize piston 26. The gear 32 being rotated by rack 30 as a result ofpiston 26 movement establishes an output position signal as a linearfunction of engine rotational speed in accordance with the relationshipset forth in equation (II). The roller 104 may be adjusted by securingthe threaded stem 1 14 in or out as required to establish linearityaccuracy.

In the event of a decrease in engine speed and a corresponding reductionin force F the above related sequence will be reversed causing movementof piston 26 toward the right as viewed in FIG. 1. However, regardlessof the relative change in engine speed, the resulting variation in forceF will cause the piston 26 to assume a position y relative to the pivotaxis of lever 54 which position is a linear function of engine speed.

Referring to FIG. 2, the effective lever arm of lever 126 through whichthe constant force of spring 94 acts is varied by roller 116 in responseto variations in temperature imposed on condition responsive device 124such that the constant reference force F against which the force F isreferenced is modified to provide the engine speed N corrected fortemperature function set forth in equation l5 It will be recognized thatthe condition responsive device 124 may be responsive to a variablecondition of operation other than temperature as, for example, anengine'operating pressure or the like.

It will be noted that the input force, F vs. piston 26 position, y, maybe varied as indicated by the curves corresponding to I" y y or F y yfor control purposes by suitable variation of the lever arm ratio 1 inthe manner disclosed in equations (9) and (10). Furthermore, it will berecognized that the input force F may have a linear relationship with anengine operating condition from which it is derived in which case theoutput position of piston 26 will vary as a square root function of theengine operating condition as shown in FIG. 4.

The embodiment of Flg. 1 may be readily adapted for use as a fluid flowmeter wherein the flow through a fluid restriction, not shown, of knownarea is measurable as a function of the square root of the pressure dropthereacross. To that end, the centrifugal weights 68 and associated stem62 of FIG. 1 may be deleted and replaced by a bellows or the likeresponsive to the pressure drop across the restriction in which case theoutput force of the bellows defines force F The resulting position ofpiston 26 is a function of the square root of the output force derivedfrom the pressure drop across the restriction and thus flowtherethrough.

Referring to FIG. 5, the embodiment shown therein is similar to FIG. 1modified to establish an output position signal which is a function ofthe square of an input position signal. Structure common to FIGS. 1 and5 is identified by the same numeral. The lever 84 is connected via alink 134 to and actuated by a rack member 136 slidably secured to casingand driven by a spur gear 138 rotatably mounted on a fixed support 140.A movable control lever 142 suitably secured to spur gear 138 is adaptedto rotate the same. The piston 26 is co'rinected via shaft 28 and link92 to roller means 144 interposed between lever 54 and a plate 146which, like plate 98, is pinned for pivotal movement on an associatedfixed support 100. A compression spring 148 interposed between plate 146and an adjustable spring retainer 150 threadedly engaged with casing 20imposes a predetermined constant reference force against plate 146. Aplurality of temperature responsive discs or capsules 152 may beinterposed between spring 148 and retainer 150 to compensate for thetemperature effect of the fluid surrounding spring 148.

The relationship set forth in equations (1) through (14) hold true inthe embodiment of FIG. 5 except that, unlike FIG. 1 wherein force F isvariable, and acts through a fixed lever arm l the force F in FIG. 5 isconstant and the effective lever arm 1 through which the force F acts isvariable. Assuming the lever arm ratio l /x to be I and the lever 84 tobe in a position where roller is aligned with roller 104, and I is equalto x, it will be noted that the force applied by roller 80 against lever54 is equal to F x/x or F The force moment on lever 54 is F,y wherein ydesignates the input position of rack member 136 relative to the pivotaxis of lever 54. For a balanced condition of lever 54, F y is opposedby an equal force moment defined by F 1 Assuming the forces F and F R tobe equal, the position of piston 26 which establishes the position ofroller means 144 relative to the pivot axis of lever 54 and thus leverarm is equal to l, and equals the square of I, or the square root of oneequals one.

Now assuming the control lever 142 is advanced to the position shown inFIG. 5 where rack member 136 occupies a position corresponding to twounits, the lever 84 moves accordingly causing a corresponding increasein lever arms 1 and y to two units each. The force imposed by roller 80on lever 54 is equal to F 2x/x or 2F 1 and the corresponding forcemoment is 2F y which unbalances the lever 54 in a counter clockwisedirection as viewed in FIG. 5 causing flapper valve 52 to move in anopening direction and a corresponding drop in pressure P,. The piston 26responds to the P P pressure differential causing roller means 144 tomove away from the pivot axis of lever 54 and increase the length oflever arm 1 Since y is equal to two units, 2F y equals 4F The opposingforce moment F 1 must equal 4F 1 to balance lever 54. Since F and F areequal, the lever arm 1 must increase to four units to establish therequired force moment balance on lever 54 which, in turn, causesstabilization of piston 26. Thus, the position of piston 26 isrepresentative of the input of two units squared. The gear 32 actuatedby piston 26 provides the required output position signal.

It will be recognized that the control lever 142 may be advanced orretarded to cause a corresponding increase or decrease in the inputlever arm 1 and a corresponding force moment unbalance on lever 54. Inany event, the resulting displacement of piston 26 to reestablish aforce moment balance on lever 54'is equal to the square of the inputposition signal established by control lever 142. v

If desired, an output pressure signal instead of an output positionsignal may be obtained from the embodiment of FIG. 5. To that end, thepiston 26, roller means 144 as well as plate 146, spring 148 andretainer 150 may be deleted and replaced by a pressure responsivemember, not shown, connected to impose a force on lever 54 in oppositionto the force imposed by roller 80. The pressure responsive member may beresponsive to a fluid pressure suitably controlled by flapper valve 52such that the output force derived from the pressure responsive membervaries as required to maintain a force moment balance on lever 54. Thecontrolled fluid pressure imposed on the pressure responsive member maybe sensed to provide an output'pressure or force signal which is afunction of the square of the input position signal of control lever142.

I claim:

1. A force moment balance lever system comprising:

a first lever mounted on a fixed support for pivotal movement thereon;

a second lever having spaced apart first and second portions engageablewith a fixed support and said first lever, respectively;

first force producing means operatively connected to said first leverfor imposing a force thereon;

second force producing means operatively connected to said second leverfor imposing a reference force thereon in opposition to said first forceproducing means;

positionable means operatively connected to said second lever foractuatlng the same relative to the pivot axis of said first lever tovary the effective lever arm of said first lever through which saidreference force acts and the effective lever arm of said second leverthrough which said first force producing means acts.

2. A force moment balance lever system as claimed in claim 1 wherein:

said second force producing means exerts a substantially constantreference force on said second lever.

3. A force moment balance lever system as claimed in claim 1 wherein:

said first force producing means is a variable input force;

said positionable means being operatively connected to said first leverand actuated in response to a force moment unbalance on said first levercaused by a change in said input force;

said positionable means being operatively connected to said second leverfor actuating the same to establish an equal force moment on said firstlever in opposition to said variable input force;

said positionable means providing an output signal as a function of thesquare root of said input force.

4. A force moment balance lever system as claimed in claim 1 wherein:

an input signal is established by a movable control member operativelyconnected to said second lever for actuating the same to cause a forcemoment unbalance on said first lever;

said first force producing means has a substantially constant outputforce and said operative connection with said first lever includes amovable force transmitting member positionable along said first lever;

said positionable means being operatively connected to said first leverand actuated in response to said force moment unbalance thereon;

said positionable means being operatively connected to said forcetransmitting member for actuating the same to vary the effective momentarm of said first lever through which said first force producing meansacts to establish a force moment balance on said first lever;

said positionable means providing an output position signal as afunction of the square of said input signal.

5. A force moment balance lever system as claimed in claim 1 wherein:

said first and second force producing means are spring means providing asubstantially constant output force.

6. A force moment balance lever system for controlling an output controlsignal as a predetermined function ofa variable input force signalcomprising:

a first pivotally mounted lever responsive to said variable input force;

positionable means operatively connected to said first lever andactuated in response to a force moment unbalance thereon caused by achange in said input force;

a second lever having spaced apart first and second portions engageablewith a fixed support and said first lever, respectively; I

said second portion being adapted to impose a variable reference forceagainst said first lever in opposition to said input force;

force producing means for generating a predetermined constant referenceforce;

force transmitting means operatively connected to said force producingmeans and said second lever for imposing said constant reference forceon said second lever;

said second lever being actuated by said positionable means to therebydisplace said first and second portions along said fixed support andsaid first lever, respectively, thereby varying the effective moment armof said second lever through which said constant reference force actsand the effective moment arm of said first lever through which saidvariable reference force acts in opposition to said input force toestablish a force moment balance on said first lever in response towhich said positionable means is stabilized.

7. A force moment balance lever system as claimed in claim 6 wherein:

said input force acts against said first lever through a fixed effectivemoment arm relative to the pivot axis of said first lever.

8. A force moment balance lever system as claimed in claim 6 wherein:

said force producing means is defined by a compression spring.

9. A force balance lever system as claimed in claim 6 wherein: I

said first and second levers are parallel;

said second lever being actuated in a direction perpendicular to thepivot axis of said first lever.

10. A force moment balance lever system as claimed in claim 6 wherein:

said positionable means includes a fluid pressure differentialresponsive piston responsive to variations in a controlled fluidpressure; and

valve means operatively connected to said first lever and actuatedthereby to vary said controlled fluid pressure and thus the position ofsaid piston.

l 1. A force moment balance lever system as claimed in claim 6 wherein:

said first and second portions are defined by first and second rollermeans rotatably secured to said I second lever in fixed spaced apartaxial relationship.

12. A force moment balance lever system as claimed in claim 1 1 wherein:

said fixed support is defined by a fixed track along which said firstroller is adapted to roll thereby providing a pivot for said secondlever. 13. A force moment balance lever system as claimed in claim 6wherein:

said positionable means is positioned as a square root function of saidvariable input force. 14. A force moment balance lever system as claimedin claim 11 wherein:

said force transmitting means is defined by roller means rotatablysecured to an adjustable support and positionable thereby along saidsecond lever and perpendicular to the pivotal axis of said first rollerto vary the effective lever arm through which said constant referenceforce acts for control calibration. 15. A force moment balance leversystem as claimed in claim 6 wherein:

said force transmitting means includes a third lever pivotally securedto a fixed support; first roller means interposed between said forceproducing means and said third lever for imposing said constantreference force on said third lever; condition responsive meansresponsive to a variable condition of operation operatively connected to,said roller means for actuating the same along said third lever tothereby vary the effective lever arm of said third lever through whichsaid constant reference force acts; second roller means interposedbetween said third lever and said second lever and operatively connectedto an adjustable support adapted to position said second roller meansalong said second lever and perpendicular to the pivotal axis of saidsecond lever to vary the effective lever arm of said second leverthrough which said reference force imposed by said second roller acts.16. A force moment balance lever system as claimed in claim 8 andfurther comprising:

a fixed spring retainer; a pivotally mounted spring retainer; saidcompression spring being interposed between said fixed and pivotallymounted spring retainers; and temperature responsive means interposedbetween said fixed retainer and said compression spring and responsiveto'the temperature of fluid surrounding said compression spring andadapted to compensate for temperature variation effects on the springrate of said compression spring.

1. A force moment balance lever system comprising: a first lever mountedon a fixed support for pivotal movement thereon; a second lever havingspaced apart first and second portions engageable with a fixed supportand said first lever, respectively; first force producing meansoperatively connected to said first lever for imposing a force thereon;second force producing means operatively connected to said second leverfor imposing a reference force thereon in opposition to said first forceproducing means; positionable means operatively connected to said secondlever for actuatIng the same relative to the pivot axis of said firstlever to vary the effective lever arm of said first lever through whichsaid reference force acts and the effective lever arm of said secondlever through which said first force producing means acts.
 1. A forcemoment balance lever system comprising: a first lever mounted on a fixedsupport for pivotal movement thereon; a second lever having spaced apartfirst and second portions engageable with a fixed support and said firstlever, respectively; first force producing means operatively connectedto said first lever for imposing a force thereon; second force producingmeans operatively connected to said second lever for imposing areference force thereon in opposition to said first force producingmeans; positionable means operatively connected to said second lever foractuatIng the same relative to the pivot axis of said first lever tovary the effective lever arm of said first lever through which saidreference force acts and the effective lever arm of said second leverthrough which said first force producing means acts.
 2. A force momentbalance lever system as claimed in claim 1 wherein: said second forceproducing means exerts a substantially constant reference force on saidsecond lever.
 3. A force moment balance lever system as claimed in claim1 wherein: said first force producing means is a variable input force;said positionable means being operatively connected to said first leverand actuated in response to a force moment unbalance on said first levercaused by a change in said input force; said positionable means beingoperatively connected to said second lever for actuating the same toestablish an equal force moment on said first lever in opposition tosaid variable input force; said positionable means providing an outputsignal as a function of the square root of said input force.
 4. A forcemoment balance lever system as claimed in claim 1 wherein: an inputsignal is establIshed by a movable control member operatively connectedto said second lever for actuating the same to cause a force momentunbalance on said first lever; said first force producing means has asubstantially constant output force and said operative connection withsaid first lever includes a movable force transmitting memberpositionable along said first lever; said positionable means beingoperatively connected to said first lever and actuated in response tosaid force moment unbalance thereon; said positionable means beingoperatively connected to said force transmitting member for actuatingthe same to vary the effective moment arm of said first lever throughwhich said first force producing means acts to establish a force momentbalance on said first lever; said positionable means providing an outputposition signal as a function of the square of said input signal.
 5. Aforce moment balance lever system as claimed in claim 1 wherein: saidfirst and second force producing means are spring means providing asubstantially constant output force.
 6. A force moment balance leversystem for controlling an output control signal as a predeterminedfunction of a variable input force signal comprising: a first pivotallymounted lever responsive to said variable input force; positionablemeans operatively connected to said first lever and actuated in responseto a force moment unbalance thereon caused by a change in said inputforce; a second lever having spaced apart first and second portionsengageable with a fixed support and said first lever, respectively; saidsecond portion being adapted to impose a variable reference forceagainst said first lever in opposition to said input force; forceproducing means for generating a predetermined constant reference force;force transmitting means operatively connected to said force producingmeans and said second lever for imposing said constant reference forceon said second lever; said second lever being actuated by saidpositionable means to thereby displace said first and second portionsalong said fixed support and said first lever, respectively, therebyvarying the effective moment arm of said second lever through which saidconstant reference force acts and the effective moment arm of said firstlever through which said variable reference force acts in opposition tosaid input force to establish a force moment balance on said first leverin response to which said positionable means is stabilized.
 7. A forcemoment balance lever system as claimed in claim 6 wherein: said inputforce acts against said first lever through a fixed effective moment armrelative to the pivot axis of said first lever.
 8. A force momentbalance lever system as claimed in claim 6 wherein: said force producingmeans is defined by a compression spring.
 9. A force balance leversystem as claimed in claim 6 wherein: said first and second levers areparallel; said second lever being actuated in a direction perpendicularto the pivot axis of said first lever.
 10. A force moment balance leversystem as claimed in claim 6 wherein: said positionable means includes afluid pressure differential responsive piston responsive to variationsin a controlled fluid pressure; and valve means operatively connected tosaid first lever and actuated thereby to vary said controlled fluidpressure and thus the position of said piston.
 11. A force momentbalance lever system as claimed in claim 6 wherein: said first andsecond portions are defined by first and second roller means rotatablysecured to said second lever in fixed spaced apart axial relationship.12. A force moment balance lever system as claimed in claim 11 wherein:said fixed support is defined by a fixed track along which said firstroller is adapted to roll thereby providing a pivot for said secondlever.
 13. A force moment balance lever system as claimed in claim 6wherein: said positionable means is positioned as a square root functionof said variable input force.
 14. A force moment balance lever system asclaimed in claim 11 wherein: said force transmitting means is defined byroller means rotatably secured to an adjustable support and positionablethereby along said second lever and perpendicular to the pivotal axis ofsaid first roller to vary the effective lever arm through which saidconstant reference force acts for control calibration.
 15. A forcemoment balance lever system as claimed in claim 6 wherein: said forcetransmitting means includes a third lever pivotally secured to a fixedsupport; first roller means interposed between said force producingmeans and said third lever for imposing said constant reference force onsaid third lever; condition responsive means responsive to a variablecondition of operation operatively connected to said roller means foractuating the same along said third lever to thereby vary the effectivelever arm of said third lever through which said constant referenceforce acts; second roller means interposed between said third lever andsaid second lever and operatively connected to an adjustable supportadapted to position said second roller means along said second lever andperpendicular to the pivotal axis of said second lever to vary theeffective lever arm of said second lever through which said referenceforce imposed by said second roller acts.